The long-term objective is to describe and elucidate the photopic abnormalities that occur in a variety of human visual disorders. This objective is pursued in a psychophysical study of patients afflicted with a retinal disease such as retinitis pigmentosa, Stargardt's macular dystrophy, cone dystrophy, congenital achromatopsia, or with a cortical disorder, for example, acquired from a head injury. The principal measurements consist of Stiles' two-color thresholds and color matches. The understanding of the functional abnormalities which we expect to accrue can contribute to the development of more sensitive diagnostic methods as well as to a better understanding of the underlying pathology.